Sensor Selection for Selective Clutch Fault Isolation in Automatic Transmissions Based on Degree of Fault Tolerance

Multiple clutches are engaged to achieve a specific gear ratio in an automatic transmission (AT). When an engaged clutch loses pressure during the AT operation, it is classified as a clutch stuck off fault. Automatic transmissions can enter in neutral states because of these faults and the vehicle can lose power at the wheels. Our previous work describes a systematic way of performing sensor placement analysis for diagnosis of clutch faults in automatic transmissions. In this paper, we approach the issue from the point of view similar to that of functional safety according to the ISO 26262 standard; where a transmission functional safety concept should address transitioning to a safe state in case of hazards associated with stuck off clutches. We try to address the questions whether all the faults really need to be isolated from each other and whether it is possible to isolate only a subset of faults to reduce the number of required sensors and still maintain a reasonable performance/safety. A way to classify clutch faults based on fault tolerant actions and the degree of fault tolerance is described. A structural analysis-based approach is then used to answer the question of sensor placement for selective fault isolation. The proposed approach is applied to a 10-Speed automatic transmission as an example. The paper concludes by demonstrating the effectiveness of selective fault isolation and discusses other applications of the approach.